On the superfield effective potential in three dimensions

We develop the superfield approach to the effective potential in three dimensions and calculate the one-loop and two-loop Kählerian effective potential in commutative and noncommutative cases.     

The Influence of Hydrogen Loading Temperature on the Mechanical Strength of Optical Fibers

The influence of hydrogen loading temperature on the mechanical strength of optical fibers is investigated. Fibers subjected to high-pressure hydrogen loading at different temperatures were submitted to bend tests, and the results compared with those for pristine fibers. The Weibull probability distribution function was used to analyze the data of the mechanical bending strength of the fibers. Fiber strength is reduced by the presence of hydrogen, and this decrease is greater for higher hydrogen loading temperatures. The mechanical properties of the polymers used to coat fibers are affected by the hydrogen loading process and also by the increase in temperature. However, there is no evidence of cracks formation that might allow water to penetrate to the surface of the glass. Observation using scanning electron microscopy revealed that the morphology of fractures in nonhydrogen-loaded fibers have distinct fracture characteristics to that of fibers that are hydrogen loaded at 90°C and 120°C.     

Gravitational geometric phase in the presence of torsion

We investigate the relativistic and non-relativistic quantum dynamics of a neutral spin-1/2 particle subject to an external electromagnetic field in the presence of a cosmic dislocation. We analyze the explicit contribution of the torsion in the geometric phase acquired in the dynamics of this neutral spinorial particle. We discuss the influence of the torsion in the relativistic geometric phase. Using the Foldy–Wouthuysen approximation, the non-relativistic quantum dynamics is studied and the influence of the torsion on the Aharonov–Casher and He–McKellar–Wilkens effects are discussed. An erratum to this article can be found at     

Li‐doped nanosized TiO2 powder with enhanced photocalatylic acivity under sunlight irradiation

This work reports on the synthesis of Li‐doped TiO₂ nanoparticles using the sol–gel process and solid‐state sintering, and investigates their potential use as a photocatalyst for degradation under sunlight excitation of different organic model compounds in aqueous solution. The structure of the nanocrystals was examined by X‐ray diffraction, UV‐vis ground state diffuse reflectance absorption spectra and X‐ray photoelectron emission spectroscopy. Results showed that samples prepared by sol–gel process and calcined at 400 °C are composed of a mixture of anatase and rutile phases, in contrast to the one prepared by solid‐state sintering, which exhibits an anatase phase with Li being involved in a spinel phase. The photocatalytic degradation of aqueous solutions of different aromatic compounds was successfully achieved under sunlight excitation in presence of Li‐doped TiO₂ prepared via sol–gel process. It was shown that the calcination temperature and the preparation mode greatly affect the photocatalytic efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

The production and destruction of the C-related 969 meV absorption band in Si

Data are reported on the production of the 969 meV absorption line as functions of the carbon concentration and radiation dose in FZ and CZ silicon. With increasing dose of 2 MeV electrons the absorption first increases and then decreases. Simple equations are presented which describe the growth and decay. It is shown that, in favourable circumtances, carbon concentrations as low as 10¹⁴ cm⁻³ can be detected in silicon by means of the 969 meV absorption line. We verify that the 969 meV line anneals out at temperatures >500 K but may increase between 450 and 500 K. We show that the increase is largest in samples irradiated at room temperature to a small dose relative to the carbon concentration.     

Sol-Gel Synthesis of Transparent Alumina Gel and Pure Gamma Alumina by Urea Hydrolysis of Aluminum Nitrate

-Alumina was synthesized by a sol-gel method with the aluminum ion hydrolysis control performed by urea. The initial saturated Al³⁺/urea solution presented urea coordinated with the aluminum ion, as shown in the ¹³C NMR and ²⁷Al NMR spectra and longitudinal relaxation times, T ₁, from the latter. The substitution of water molecules in the Al³⁺ coordination shell by urea controlled the hydrolysis process and provided an extensive nucleation during the initial steps of the aluminum hydroxide formation due to urea thermolysis at 90°C. The resulting sol, composed of Al(OH)₃ nanoparticles, coalesced and became a transparent gel permeated by a solution of urea and the polycation ion [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺. The freshly prepared gel was transformed, under heating at 300°C, directly to -alumina, characterized by FTIR, ²⁷Al-MAS-NMR and S_BET techniques, without - or -phases, as a consequence of the high degree of homogeneity of the -alumina precursor.     

Stable transition layers in a semilinear diffusion equation with spatial inhomogeneities in N-dimensional domains

We prove existence and establish the asymptotic behavior, as ε→0, of stable stationary solutions to the equation u_t=ε∇·[d(x)∇u]+(1−u²)[u−a(x)], for , where , N?2, with Neumann boundary condition. The function a(x)∈C0,ν(Ω) satisfies −1<a(x)<1 and vanishes on some hypersurfaces. The results generalize to N-dimensional domains and to variable diffusivity earlier paper by Angenent et al. (J. Differential Equations 67 (1987) 212).     

Rigidity Theorems for Manifolds with Boundary and Nonnegative Ricci Curvature

In this paper, we obtain some rigidity theorems for compact Riemannian manifolds Ω with boundary M and nonnegative Ricci curvature; for instance, we prove that the existence of certain functions on M together with a lower bound c > 0 on the principal curvtures of M imply that Ω is an euclidean ball of radius $ {1\over c} $ .     

Some existence and nonexistence theorems for compact graphs of constant mean curvature with boundary in parallel planes

Given H≥0 and bounded convex curves α₁, ...,⇌_n, α in the plane z=0 bounding domains D₁, …, D_n, D, respectively, with if i ∈ j and with D_i ⊂ D, we obtain several results proving the existence of a constanth depending only on H and on the geometry of the curves α_i, α such that the Dirichlet problem for the constant mean curvature H equation: where may accept or not a solution.     

Ion larmour radius effect on rf ponderomotive forces and induced poloidal flow in tokamak plasmas

Analytical approximations are used to clarify the effect of Larmour radius on rf ponderomotive forces and on poloidal flows induced by them in tokamak plasmas. The electromagnetic force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation. The first part, called the gradient electromagnetic stress force, is combined with fluid dynamic (Reynolds) stress force, and gyroviscosity is included into viscosity force to model finite ion Larmour radius effects in the momentum response to the rf fields in plasmas. The expressions for the relative magnitude of different forces for kinetic Alfven waves and fast waves are derived.